Publications

• Biosynthesis of colitose: expression, purification, and mechanistic characterization of GDP-4-keto-6-deoxy-D-mannose-3-dehydrase (ColD) and GDP-L-colitose synthase (ColC).

  Alam J., Beyer N., Liu H.W.

  L-Colitose is a 3,6-dideoxyhexose found in the O-antigen of Gram-negative lipopolysaccharides. To study the biosynthesis of this unusual sugar, we have cloned and sequenced the L-colitose biosynthetic gene cluster from Yersinia pseudotuberculosis VI. The colD and colC genes in this cluster have be ... >> More

  L-Colitose is a 3,6-dideoxyhexose found in the O-antigen of Gram-negative lipopolysaccharides. To study the biosynthesis of this unusual sugar, we have cloned and sequenced the L-colitose biosynthetic gene cluster from Yersinia pseudotuberculosis VI. The colD and colC genes in this cluster have been overexpressed and each gene product has been purified and characterized. Our results showed that ColD functions as GDP-4-keto-6-deoxy-D-mannose-3-dehydrase responsible for C-3 deoxygenation of GDP-4-keto-6-deoxy-D-mannose. This enzyme is coenzyme B(6)-dependent and its catalysis is initiated by a transamination step in which pyridoxal 5'-phosphate (PLP) is converted to pyridoxamine 5'-phosphate (PMP) in the presene of L-glutamate. This coenzyme forms a Schiff base with the keto sugar substrate and the resulting adduct undergoes a PMP-mediated beta-dehydration reaction to give a sugar enamine intermediate, which after tautomerization and hydrolysis to release ammonia yields GDP-4-keto-3,6-dideoxy-D-mannose as the product. The combined transamination-deoxygenation activity places ColD in a class by itself. Our studies also established ColC as GDP-L-colitose synthase, which is a bifunctional enzyme catalyzing the C-5 epimerization of GDP-4-keto-3,6-dideoxy-D-mannose and the subsequent C-4 keto reduction of the resulting L-epimer to give GDP-L-colitose. Reported herein are the detailed accounts of the overexpression, purification, and characterization of ColD and ColC. Our studies show that their modes of action in the biosynthesis of GDP-L-colitose represent a new deoxygenation paradigm in deoxysugar biosynthesis. << Less

  Biochemistry 43:16450-16460(2004) [PubMed] [EuropePMC]

  This publication is cited by 6 other entries.

• A structural study of GDP-4-keto-6-deoxy-D-mannose-3-dehydratase: caught in the act of geminal diamine formation.

  Cook P.D., Holden H.M.

  Di- and trideoxysugars are an important class of carbohydrates synthesized by certain plants, fungi, and bacteria. Colitose, for example, is a 3,6-dideoxysugar found in the O-antigens of Gram-negative bacteria such as Escherichia coli, Salmonella enterica, Yersinia pseudotuberculosis, and Vibrio c ... >> More

  Di- and trideoxysugars are an important class of carbohydrates synthesized by certain plants, fungi, and bacteria. Colitose, for example, is a 3,6-dideoxysugar found in the O-antigens of Gram-negative bacteria such as Escherichia coli, Salmonella enterica, Yersinia pseudotuberculosis, and Vibrio cholerae, among others. These types of dideoxysugars are thought to serve as antigenic determinants and to play key roles in bacterial defense and survival. Four enzymes are required for the biochemical synthesis of colitose starting from mannose-1-phosphate. The focus of this investigation, GDP-4-keto-6-deoxy-d-mannose-3-dehydratase (ColD), catalyzes the third step in the pathway, namely the PLP-dependent removal of the C3'-hydroxyl group from GDP-4-keto-6-deoxymannose. Whereas most PLP-dependent enzymes contain an active site lysine, ColD utilizes a histidine as its catalytic acid/base. The ping-pong mechanism of the enzyme first involves the conversion of PLP to PMP followed by the dehydration step. Here we present the three-dimensional structure of a site-directed mutant form of ColD whereby the active site histidine has been replaced with a lysine. The electron density reveals that the geminal diamine, a tetrahedral intermediate in the formation of PMP from PLP, has been trapped within the active site region. Functional assays further demonstrate that this mutant form of ColD cannot catalyze the dehydration reaction. << Less

  Biochemistry 46:14215-14224(2007) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.